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THERE has been no lack of activity during the past few months in the various departments of the applied science of engineering. In the arts of war and of peace alike, the direction of the sources of power in nature to do things which would be impossible to the unaided strength of man has been conspicuously effective.
Many of the most notable examples of modern engineering work contain nothing new in themselves, their real claim to attention being the extension of well-known principles and structures to much greater limits than were originally intended or imagined. The mere making a thing bigger, or swifter, or heavier may seem a simple matter of degree; but the engineer knows that with such extension of scope or action a number of new elements are introduced, rendering past experience of limited value as a guide of conduct.
Thus, one of the engineering problems at present under active discussion is the operation of machinery for hoisting ore and material from great depths in the earth. To the layman a mine hoist consists of a drum around which a rope is wound for the purpose of lifting a cage or a bucket from a hole in the ground a mere extension of the ancient windlass. If the hole has to be made deeper, it simply takes more rope and a larger drum. But these two things mean also greater weight to be lifted, and greater inertia forces at starting and stopping. Some mines are to-day operated at a depth of a mile below the surface, and greater depths are already being demanded to reach ore deposits of large extent and value.
These requirements have recently led to active discussions of the extent to which the limitations of hoisting apparatus may affect the operations of such deep mines. Steel wire cables are at present the most available means of reaching down to such depths; but by the time a depth of a mile and a half is attained the whole strength of even a steel cable is required to sustain its own weight, and no further load can safely be added. As the rope is wound up, this weight is diminished, so that great variations in load are thrown upon the winding
engines; and when these and the inertia changes are to be considered, the mere expression of their relations involves complicated algebraic equations.
Various plans have been proposed for overcoming these difficulties in order that deep mining operations may not be limited. At the present time the method of dividing the lift into two or more stages is regarded with some favor; but this involves the delays and cost of reloading as well as the installation of winding engines underground. This latter objection may be met in part by the use of electric motors, the current being transmitted from a power house at the surface. Some such system will probably be adopted in certain localities. A more scientific method which has been recently suggested is to do away entirely with the hoisting rope, and mount the motive power directly upon the cage to be lifted. In this case an electric motor would drive gear wheels engaging in racks on the sides of the vertical shaft; the whole thus forming a vertical rack railway, the current being transmitted from above through some form of sliding contact. Such an apparatus would be practically independent of the depth of the shaft, there being no more weight to be lifted at the bottom than at the top; and the vertical distance would have no more influence upon its action than the length of a trolley line has upon its operation. The speed attainable with such a device might be less than that of a cable hoist; but for very deep shafts it may yet be found the most available system.
After a long and successful career as a fundamental principle in the construction of machines for dealing with fluids, steam engines, pumps, blowing engines, etc., the piston reciprocating in a cylinder appears to be in a fair way to be ousted from its ancient eminence. Rotary motion, at high and higher speeds, is being applied to all purposes wherever practicable, and success in each application leads to further and wider extensions. The first steam engines were made to operate reciprocating pumps in mines, and nothing was more natural than that a vertical cylinder should be connected to a beam overhanging the mouth of the pit down which the pump was situated. When, later on, it was attempted to use the engine to drive revolving machinery, the pump was replaced by a crank; and even yet the superfluous beam is retained in situations where it is of no more use than the two buttons on the back of a man's coat.
With the advent of the steam turbine, however, the possession of an efficient steam engine of high rotative speed has called attention to the
advantages which the direct applications of such a motion possess. Thus, the centrifugal pump has, until recently, been considered mainly applicable to the elevation of large volumes of water at low lifts, and its advantages for such service are undoubted. One of the special features of such pumps is the fact that the water flows continuously in the same direction, all shocks and reversals involved in the action of the reciprocating piston pump being absent. Until recently, however, centrifugal pumps have not been available for high heads, and special forms of plunger pumps have been constructed for this duty. By connecting a suitably designed centrifugal pump directly to the spindle of a steam turbine, the advantages of a high rotative speed appear. The great velocity attained enables even a single wheel to deliver water against heads of 150 metres, while by arranging several wheels upon the same shaft, each delivering the water to the next, a continuous flow is maintained at an elevation as great as 500 metres above the pump.
In like manner, the development of the steam turbine has led to modifications in the design of dynamo-electric machines. The early dynamos demanded high rotative speeds, and numerous efforts were made to construct high-speed reciprocating engines to meet this requirement. The superior economy of the slower engines, however, led to the design of the large, slower-running alternators now in general use in the large power stations, and central-station practice generally has been governed accordingly. The high speed of the turbine now bids fair to transform this department of engineering work, since the small, directconnected dynamo forms, with the turbine, a generating set of power, compactness, and convenience which makes it especially satisfactory. It is believed that but few more of the great reciprocating engines will be built for the electric power house.
High rotative speeds almost equal to those of the steam turbine are attained by the small reciprocating gasoline engines used upon automobiles, motor boats, and dirigible balloons, and some of these small machines develop a surprising amount of power for their weight and size. This high power is mainly due to the high speed, and this fact has led to the design of a simple and practical apparatus for measuring the power developed by such motors. In the case of larger and more slowly moving motors, and of steam engines, it is possible to attach the indicator to the cylinder and measure the mean effective pressure from which the power is developed; but no indicator can be used at the speeds common upon automobile motors. The new device, designed by
Colonel Renard, himself early identified with the development of dirigible balloons in France, consists simply of a pair of arms, carrying flat vanes, and forming a sort of windmill attached to the shaft of the motor to be tested. At such high rotative speeds as are encountered with these machines the resistance of the air becomes very great, so that the entire power developed by the motor is required to maintain the speed, and the size of the windmill which can be driven thus affords a measure of the power of the motor. Colonel Renard has arranged such a windmill, with square flat vanes, which can be adjusted to different distances from the shaft upon the arms. The arms being graduated by trial, the power absorbed for any given speed may be tabulated for each position. To test the power of a motor it is only necessary to attach the windmill to the shaft, and, by successive trials, adjust the vanes to such a distance on the arms as will hold the motor to its proper speed at full power. The power then developed is at once known, by reference to the table of tests made when the windmill was calibrated; this calibration being previously effected by driving the windmill at various speeds by an electric motor and measuring the current required. By such methods the performance of small internal-combustion motors is being critically studied; and every effort is being made to increase the power without a corresponding increase in weight, this being the great aim in connection with aerial navigation.
Until recently the motor boats to which small internal-combustion engines are fitted have been regarded principally as pleasure craft, intended for high speeds, racing, and sporting events. The convenience. of such boats over the ordinary steam launch has led to their consideration for more useful purposes in connection with the work of naval vessels, harbor service, and similar duty. There has been some reluctance, however, to introduce motor boats into regular service because of a feeling among naval officers, shipowners, and harbor authorities that these little vessels were lacking in endurance and reliability. To determine these points, there has lately been held in England, with some interesting results, a series of reliability trials, under the auspices of a committee of well-known engineers, in connection with the Automobile Club. The tests involved the continuous operation of the boats under trial, over a selected course, for ten hours of each of two consecutive days, making a total run of twenty hours. Every stop was charged against the record of a boat, and questions of reliability and continuity of action were made foremost in determining awards; speed, economy,
and safety also being taken into account. The results appear to have been very satisfactory. Out of sixteen boats entered but two failed to fulfil the requirements of the test. The satisfactory use of such boats in commercial and naval service will naturally lead to improved designs for such duty, and this may prove the entering wedge to open this department of work for the admission of internal-combustion motors for larger boats. It is evident that for such larger motors some less expensive fuel than benzine or gasoline must be used; but there are several engines in which kerosene has been successfully employed. In the Diesel motor even crude petroleum is completely burned.
Although efforts to prevent the production of smoke in the combustion of bituminous coal have been earnestly made ever since the days of Watt, the smoke nuisance is still with us. In the case of stationary power plants, the evil may frequently be minimized by mere dilution of the gases with such an excess of air as to render the discoloration less noticeable; but in the great majority of cases any attempt to reduce the quantity of smoke lowers the economy of the plant. At the present time, however, the principal source of trouble is found in the use of bituminous coal upon steam locomotives, the trails of smoke emitted having a most injurious effect upon the prosperity of the communities upon which the railways must depend for much of their business. No effective means can be found for the prevention of smoke when bituminous coal is burned at such rapid rates, in such contracted furnaces, and in such close proximity to cooling surfaces. It is admitted that the only way to prevent the production of smoke by steam locomotives is found in the use of a smokeless fuel, such as anthracite or coke. The cost of this remedy is prohibitory, except within certain limited localities, so that relief must be sought from an entirely different source. The use of electric power upon railways has been discussed from various standpoints, but of the advantage of its absolute freedom from smoke along the line there can be no doubt. The power houses may be placed at points where their smoke will do little or no harm, while the cleanliness of the line itself by the increased business which will be attracted will do much to make up for the cost of the change. It is only by the use of electric driving that the many schemes for tunnels and subways can be made tolerable, and the experience which will thus be gained should hasten the transformation of the entire motive power systems of main lines.
An important department of railway traffic is the transport of perish